In the discussion that follows, reference is made to certain structures and/or methods. However, the following references should not be construed as an admission that these structures and/or methods constitute prior art. Applicants expressly reserve the right to demonstrate that such structures and/or methods do not qualify as prior art.
According to the American Diabetes Association, diabetes is the fifth-deadliest disease in the United States and kills more than 213,000 people a year, the total economic cost of diabetes in 2002 was estimated at over $132 billion dollars, and the risk of developing type I juvenile diabetes is higher than virtually all other chronic childhood diseases.
A critical component in managing diabetes is frequent blood glucose monitoring. Currently, a number of systems exist for self-monitoring by the patient. Most fluid analysis systems, such as systems for analyzing a sample of blood for glucose content, comprise multiple separate components such as separate lancing, transport, and quantification portions. These systems are bulky, and often complicated and confusing for the user. The systems require significant user intervention.
Technology development in the field of self-monitoring of blood glucose has placed the burden of acquiring sufficient blood for conducting a test on the user of the technology. Historically, diabetics have been taught to lance their finger tips to produce blood for conducting the test. Ironically, the fingers are not only one of the most sensitive body parts to pain, but they also are among the areas of skin that are most highly perfused with blood. Earlier versions of consumer-oriented self-monitoring products usually required many microliters of blood, and the finger tips provided a reasonably convenient area to lance that would be most likely to produce the required volume of blood.
More recently, some self-monitoring systems offer the option to the user to test at alternate sites such as the palm, forearm, or thigh. While these sites are generally known to be significantly less sensitive to the pain associated with lancing, the adoption of alternate site testing has been limited for at least four reasons: 1) only a few meter products have been approved by the FDA for testing at alternate sites at this time; 2) many testers do not know that they can use their device at the alternate sites; 3) many testers find it relatively difficult to express sufficient blood at the alternate sites to perform a test; 4) data published in medical literature on some of the meters shows that there is a distinct difference between glucose levels measured at alternate sites relative to the finger, particularly when glucose levels are falling and/or the subject may be hypoglycemic. Consequently, there is a perception by the medical community that there may be an increased risk for delayed or improper treatment by the diabetic if they act only on the basis of glucose levels measured from alternate sites. Thus, the finger lancing site remains the most frequently used test site by far.
Lancing devices and the lancets themselves have also evolved somewhat over the past few decades. Some lancing mechanisms may produce relatively less pain by either 1) projecting the lancet in and out of the skin in a more straight path and thus reducing stimulation of percutaneous nerves which provide the pain stimulus; and 2) offering depth control in the lancing device so that the user may balance the expression of sufficient blood against the level of pain. Furthermore, lancet manufacturers offer a variety of lancet sizes, lengths, and tip bevel patterns with some companies claiming that their lancet is less painful than others.
What remains clear is that the most testers, when lancing at the finger, often must put down the lancing device and apply pressure near the finger tip in order to produce sufficient blood for the test strip in the meter. Many instructions for use with conventional meter systems specifically prescribe that the user perform this “milking” process because without it, many will not spontaneously produce the required volume. Applicants have observed this phenomenon in the use of commonly available commercial sampling and meter systems. When a trained professional lanced the finger tips of 16 volunteer diabetic subjects at the maximum depth setting on commercially available device under controlled conditions, only 15% of lanced sites spontaneously produced sufficient blood for the meter to accurately measure glucose levels.
An engineering model of the lancing wound and of the process for expressing blood to the skin surface provides insight into why the milking process is so often a requisite to successful testing of blood glucose levels. The most commonly recommended site for testing by self-monitoring meter manufacturers is the soft tissue pad on the dorsal side of the distal finger tip. Once a wound is created by the lancing device, a pathway in the soft tissue communicates between the surface of the skin and the damaged blood vessels below the epidermal skin layers. From the perspective of engineering fluid dynamics, this pathway can be considered as a pipe or channel between the reservoir of blood and the surface of the skin.
This pipe, however, often does not remain sufficiently open to permit adequate blood flow largely because of the elastic recoil generated by the extracellular collagen in the skin. Fluid dynamics predicts that a sufficiently large pressure differential must exist across a pipe in order for flow to occur and that the requisite pressure is elevated as the resistance across the pathway increases. In the case of a lanced finger tip, the pressure differential is the pressure of blood below the skin (typically no more than ˜20 mmHg) relative to the pressure at the surface of the skin (typically 0 mmHg). For most individuals this low pressure gradient cannot overcome the resistance caused by the tendency of the wound pathway to close.
The manual milking process incorporates two primary biomechanical mechanisms which assist in the expression of blood to the surface of the skin. First, the pressure applied to the soft tissue near the lancing site increases the blood pressure below the skin and elevates the magnitude of the pressure gradient across the wound pathway. This is clearly visible in individuals with lighter colored skin when the finger is compressed near the distal phalangeal joint—the tissue color becomes redder as the capillary bed near the skin surface becomes engorged with blood. With the increased pressure gradient, increased blood flow is expected in rough proportion
The second mechanism arises from the deformation of the skin near the lancing site, which may tend to temporarily enlarge the wound pathway with milking. Since the resistance to fluid flow in a simple pipe or channel is proportional to the cross-sectional area of the pathway. Thus, distension of the skin via applied pressure may reduce the wound pathway resistance and enhance blood expression to the skin surface.
Attempts have been made in the past to take steps toward automation of the testing process at alternate sites. Specifically, the Sof-Tact® System offered by Medisense in the early 2000s had the capability to test automatically at alternate sites without any user intervention, but only after each lancet and test strip had been manually loaded into the device. This meter, however, is no longer available on the market.
A device similar to the Soft-Tact device is disclosed in U.S. Patent Application Publication No. 2004/0138588 A1. This device attempts to integrate all the functions required to complete a glucose test into one device. This device however still requires the user to load a lancet and a test strip prior to each individual testing event, and fails to describe a catalyst (i.e. —mechanism to stimulate or enhance expression of blood from the lanced wound site) that ensures that a sufficient sample is expressed from the wound.
This device is described in U.S. Patent Application Publication No. 2005/0010134 A1, and U.S. Pat. No. 6,793,633 B2 uses a spring, or motor driven mechanism to apply pressure around the target wound area. However, the device therein is not a fully integrated system. From the description it appears that the user must insert a new lancet and test strip assembly for each test. Another disadvantage of the device is that the device requires two hands for operation. Specifically, the user must hold the device in one hand while testing a finger on the other hand.
Another disadvantage of the device disclosed above is that for the device to function properly the user must be able to resist the downward force created by the motor/spring driven pressure applications system. In other words, as the device applies a downward force to create pressure around the target site the user must be able to hold the device flush against the skin for it to operate properly. This may present a problem for some elderly or disabled users who may not have the strength to hold the device in place as a test is performed.
Another disadvantage of the device described above is that the devices applies a force via a downward “telescoping” mechanism. A piston-like ring is pressed into the user's skin to aid in sample extraction. This type of pressure catalyst does not trap the maximum amount of blood proximal to the lancing site and thus does not generate a sufficient sample within the target area.
Thus, conventional finger tip sampling devices and methods are overly reliant upon user-dependent milking in order to consistently express a sufficient quantity of blood from the wound site.
Moreover, there is no self-monitoring system currently available that integrates the steps of lancing, expression of body fluid, transport of body fluid to the quantification apparatus, and quantification of the analyte at the finger tip in a fully automatic way. While many diabetics continue to test their blood glucose levels with blood from the finger, testing at the alternate sites offers the advantage of significantly less pain when lancing the palm, forearm, etc. Thus, it would be advantageous to have an automatic and fully integrated meter constructed for testing at both the finger and the alternate sites.